1. Field of the Invention
The present invention relates to a data receiving apparatus and a data receiving method.
2. Related Background Art
3GPP (3rd Generation Partnership Project) is working on MBMS (Multimedia Broadcast/Multicast Service) to implement the broadcast/multicast service in third-generation mobile communication systems. The MBMS provides only a downlink channel from a base station to a mobile station but provides no uplink channel from a mobile station to a base station. In digital broadcast, similarly, the service also provides only a downlink channel from a broadcast station to a receiver but provides no uplink channel from a receiver to a broadcast station.
An example of the known technologies of delivering electronic files through the use of such a unidirectional channel is FLUTE (File Delivery over Unidirectional Transport), for example, as disclosed in Non-patent Document 1 below. FIG. 14 is an illustration showing a file delivery sequence in FLUTE. In FLUTE, a data transmitter 1 first delivers a File Delivery Table (hereinafter referred to as FDT) containing attributes of electronic files to be delivered, as object ID(TOI)=0 (S10). A data receiver 2 receives the FDT delivered from the data transmitter 1, through the unidirectional channel. FIG. 15 is an illustration showing a description example of the FDT in FLUTE. The FDT contains the description in the XML format of attribute information, such as a file name, an object ID, a file type, a compression type, a data length, and a URL, about one electronic file or about each of two or more electronic files, as shown in FIG. 15. It is seen herein that the FDT shown in FIG. 15 contains the description of the attribute information of an electronic file with object ID=1 (dashed, enclosed part P1) and the attribute information of an electronic file with object ID=2 (dashed, enclosed part P2).
After delivering the FDT, the data transmitter 1 divides each electronic file into segments and delivers the segments. In the example shown in FIG. 14, the data transmitter 1 first divides the electronic file 1 with object ID=1 into a plurality of packets and delivers them (S12), and, subsequently, the data transmitter 1 divides the electronic file 2 with object ID=2 into a plurality of packets and delivers them (S14). The data receiver 2 receives the electronic files delivered from the data transmitter 1, through the unidirectional channel. Thereafter, the data receiver 2 assembles each received electronic file and transfers the assembled electronic file to an appropriate application with reference to the File Delivery Table received in advance.
FLUTE allows delivery of relatively high volume of electronic files through the unidirectional channel in accordance with the procedure as described above. In FLUTE, redundant data for restoration of the segmental data is also delivered, in addition to the segmental data forming each electronic file, so as to enable restoration of the segmental data from the redundant data even with loss of part of the segmental data, thereby ensuring a certain level of reliability.
There are also disclosed techniques of performing data delivery with high reliability also using an uplink channel. Non-patent Document 2 below describes that, during an operation of delivering an electronic file from a data transmitter to a data receiver, an uplink channel is always established for transmission of a signal from the data receiver to the data transmitter, to enable the data receiver to send a packet loss signal (NACK) through the uplink channel. Patent Document 1 below discloses such technology that after a data transmitter delivers data by multicast to a data receiver, the data receiver notifies the source data transmitter of a data part not acquired successfully, and the data transmitter again transmits the data part thus notified of, by multicast.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-124992
[Non-patent Document 1] “FLUTE-File Delivery over Unidirectional Transport,” IETF Internet Draft, draft-ietf-rmt-flute-07.txt, December 2003
[Non-patent Document 2] Shingo Kinoshita, “Current trend of reliable multicast technology,” Transactions B of THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERS Japan, Vol. J85-B, No. 11, pp. 1819-1842, November 2002